The Influence of Litter Size on Brain Damage Caused by Hypoxic-Ischemic Injury in the Neonatal Rat

Abstract

Hypoxic ischemia is a common cause of brain injury in the human neonate. This can be mimicked in the neonatal rat, but produces variable injury. The present study investigated the influence of litter size on the severity and variability of damage caused by hypoxic-ischemic injury in neonatal rats. Groups of 7-d-old pups from birth-sized litters (13-15 pups), or from litters culled to 10 on postnatal d 2, and 8-and 9-d-old pups from birth-sized litters, were exposed to common carotid artery occlusion and then, 3 h later, hypoxia (2 h 15 min, 8% oxygen). Damage was assessed histologically 72 h after injury, and graded (I-IV) according to severity. In nonculled litters, similar numbers of animals had each grade of injury. Most pups (70%) from culled litters had grade III or IV damage, and severity was significantly greater than in nonculled litters (p Ͻ 0.001). Pups from culled litters were heavier (17.6 Ϯ 0.4 g) than pups from nonculled litters (14.7 Ϯ 0.3 g, p Ͻ 0.0001). To determine whether this indicated that culled litters were more similar to older pups in their response to hypoxic-ischemic injury, we examined injury in 8-and 9-d-old pups of similar body weight to 7-d-old pups from culled litters. The severity and distribution of damage in the older pups was different from damage in the 7-d-old pups from culled litters. These data suggest that in 7-d-old rats, litter size influences damage caused by hypoxicischemic injury, and that the relationship between body weight, brain development, and susceptibility to hypoxic-ischemic injury is complex. Hypoxic-ischemic injury in neonates occurs as a result of intrauterine hypoxia and birth asphyxia and is a significant cause of death and disability (1, 2). To study the mechanisms underlying hypoxic-ischemic injury in the laboratory setting, the injury can be mimicked in the neonatal rat (3).A commonly used animal model to study perinatal hypoxicischemic brain damage is the 7-d-old rat subjected to unilateral common carotid ligation followed by exposure to 8% oxygen (4, 5).The severity of damage caused by hypoxic-ischemic injury in the 7-d-old rat is variable, often requiring 25-30 animals per group, and a similar number of controls, to test treatments and interventions (6 -9). Variation is reportedly limited by using pups of similar body weight (10 -12), and several studies have culled litters, possibly to reduce variation in body weight (10, 13, 14), but no universal protocol has been followed. A previous study observed that pups assigned to litters of six on postnatal d 1 (P1), were more susceptible to injury on P7 than those from litters of 14 (6). However, in this study, damage was assessed by measurement of brain size.Thus, the aim of the present study was to investigate in more detail the effect of culling litters on the damage caused by hypoxic-ischemic injury in the 7-d-old rat, and to determine the relationship between body weight and injury severity in culled and nonculled litters. Pups from culled litters were found to be heavier than those from birth-size...

Biphasic changes in the levels of poly(ADP‐ribose) polymerase‐1 and caspase 3 in the immature brain following hypoxia–ischemia

“…The experimental parameters were retrospectively examined to identify factors that may have accounted for this variable response. We found that the variability could not be attributed to length of time between carotid artery ligation and hypoxia or to litter size, two factors that have been suggested to influence outcome (Dwyer et al, 1988;Oakden et al, 2002). Nutritional status is another factor that may influence susceptibility to HI.…”

“…These variables are most likely present in all studies of HI in the P7 rat as evidenced in the literature associated with this model (Ivacko et al, 1996; Puka‐Sundvall et al, 2000a; Oakden et al, 2002). One difference between our study and others that observed >90% of animals with injury is the severity of the insult.…”

Resuscitation with 21 or 100% Oxygen in Hypoxic Nicotine-Pretreated Newborn Piglets: Possible Neuroprotective Effects of Nicotine

“…These variables were taken into account as covariates in the statistical calculations without presenting a significant difference between the groups, and no correlation between these differences and the appearance of necrosis could be found. However, it is noteworthy that it has been shown that neonatal rats with heavier versus lighter body weight present more extensive post-ischemic brain damage [32] , suggesting that this parameter could influence the results despite the fact that it was included in the statistical analyses. There is also the matter of the significantly lower hemoglobin value in the saline-pretreated animals, which raises the question if nicotine-pretreated animals could have endured hypoxia for a longer time due to their higher hemoglobin values.…”

Erythropoietin Protects Dopaminergic Neurons and Improves Neurobehavioral Outcomes in Juvenile Rats after Neonatal Hypoxia-Ischemia

“…In the initial presentation of this model of HI-induced brain injury, Rice et al (2) exposed P7 rat pups to 3.5 h of hypoxia and subsequently found that Ͼ90% of animals had evidence of moderate to severe neuronal changes in the ipsilateral cortex and striatum and that 56% of animals had ipsilateral hemisphere infarctions. Other factors can also affect the degree of brain injury in this model, including carbon dioxide tension (26), energy availability (31), and litter size (23). Given the possibility that a threshold level of injury beyond which no treatment may be possible may exist, we chose a 90-min HI exposure to avoid extensive injury and thus optimize our chance of identifying subtle effects.…”